This PR brings improvements to `PDF` builds via `LaTeX` by incorporating the
[jupyterbook-latex](https://github.com/executablebooks/jupyterbook-latex

) extension.

This initial release:

1. harmonises the document structure for `html` and `latex` outputs, by implementing support for `part`/`chapter` structures in the `_toc.yml` for PDF via LaTeX,
2. brings support for the jupyter-book directive `tableofcontents` to PDF via LaTeX, and
3. adds support for commonly used tags on `code-cell` directives (such as `hide-cell`) to PDF via LaTeX

Co-authored-by: mmcky <mamckay@gmail.com>
Co-authored-by: mmcky <mmcky@users.noreply.github.com>